The broad and long-term objectives of this research program are to elucidate the neuroendocrine control systems which govern reproductive processes in a representative primate, the rhesus monkey. Of particular concern will be the mechanisms underlying the initiation of the preovulatory gonadotropin surge. In vivo approaches will use rhesus monkeys with sectioned pituitary stalks or with hypothalamic lesions maintained with chronic exogenous GnRH replacement regimens. Pituitary fragments cultured in vitro for periods in excess of one week will also be studied in this regard. The pulsatile release of gonadotropin secretion and the neuroendocrine mechanisms which govern this pattern of basal gonadotropin secretion will remain a major thrust of this investigation. The electrophysiological correlates of the circhoral discharges of gonadotropins and the antecedent release of GnRH will be investigated using recording electrodes placed in the tuberoinfundibular region of the hypothalamus. The influence of various endocrine, neural and pharmacological perturbations on this circhoral bursting mechanism, when finally identified, will then be studied.